SAN DIEGO – The San Diego County sheriff says arson will be among the many possibilities investigators will look at in trying to determine what caused nine fires to break out during a two-day heat wave.

Sheriff Bill Gore said Thursday that it could take months to find the causes of the blazes concentrated in the northwestern area of the county, from the coast to areas 10 to 15 miles inland.

The first fire started Tuesday. The eight other wildfires erupted over the course of hours Wednesday.

Gore says investigators are not ruling anything out, but he also wouldn't prejudge the investigations.

He noted that sparks from vehicles can easily ignite brush in such hot, dry and windy conditions.